1. Field of the Invention
The invention relates to an optoelectronic device, and more particularly, to an image sensor.
2. Description of Related Art
With developments and improvements in electronic products such as a digital camera, demands for image sensors consumer market are rapidly increased. Generally, an image sensor can be divided into major types including a front side illuminated image sensor and a backside illuminated image sensor.
In the front side illuminated image sensor, sensing pixels are formed on the front side of a substrate, and a metal circuit layer is disposed above the sensing pixels. An incident light needs to pass through the metal circuit layer in order to reach the sensing pixels. Due to blocking of the metal circuit layer, the light sensitivity of front side illuminated image sensor is low. In comparison with the front side illuminated image sensor, the incident light is irradiated from a back side of a substrate into the backside illuminated image sensor to reach the sensing pixels without passing through a metal circuit layer. Therefore, the backside illuminated image sensor has relatively higher light sensitivity.
However, in both the front side illuminated image sensor and the backside illuminated image sensor, when the number of sensing pixels is increased and the size of each sensing pixel is reduced, the incident light cannot be easily converged to the corresponding sensing pixel, such that the performance of the image sensor cannot be improved.